A large variety of applications in semiconductor and optoelectronics industries can benefit from development of efficient methods for forming wavelike patterns on the surface of semiconductor materials. While different applications require different degrees of coherency, the structures with higher coherency and smaller feature size are usually associated with higher performance.
A method for forming wavelike patterns upon silicon surface as a nanostructure was disclosed in Russian Patent Application RU 99124768. In this method, silicon is sputtered with a homogeneous ion flux (flow) of molecular nitrogen N2+ until a periodic wavelike nanostructure with the nanostructure wave crests orientated perpendicular to a plane of ion incidence is formed.
First, a set of parameters, defining the geometry of an emerging wavelike nanostructure and the sputtering depths Dm and DF, corresponding to the commencement and completion of the growth of nanostructure wave amplitude, is selected. This set of parameters includes ion energy, an angle of ion incidence upon the silicon surface, silicon temperature, and a depth of ion penetration into the silicon. All these parameters are selected based upon a wavelength of the nanostructure. The method uses a N2+—Si system to form a wavelike nanostructure.
It is also known that gallium arsenide sputtered with O2+ ions (O2+—GaAs system) leads to formation of a wavelike nanostructure (Karen A., Nakagawa Y., Hatada M., Okino K., Soeda F., Ishitani A. Quantitave Investigation of the O2+-Induced Topography of GaAs and other III-V Semiconductors: an STM Study of the Ripple Formation and Suppression of the Secondary Ion Yield Change by Sample Rotation.—Surf. and Interf. Anal., 1995, v. 23, p. 506-513). A useful property of the said nanostructure is a sufficiently high aspect ratio (i.e. the ratio of wave amplitude to wavelength or a wave period). However, the degree of coherency and planarity of wavelike nanostructures being formed in the O2+—GaAs system is low.
It is also known that sputtering of silicon with a flux of molecular oxygen ions (O2+—Si system) leads to a formation of a wavelike pattern structure (Vajo J. J., Doty R. E., Cirlin E. H. Influence of O2+ energy, flux and fluency on the formation and growth of sputtering-induced ripple topography on silicon.—J. Vac. Sci. Technol. A, 1996, v. 14, No 5, p. 2709-2720).
Using scanning electron microscopy (SEM) the inventors have learned that at a certain depth of the silicon sputtering Dm corresponding to the commencement of an intensive growth of amplitude of a wavelike pattern structure a low-amplitude structure pattern is formed in the O2+—Si system. These early-stage structures exhibit higher coherency and larger uninterrupted length of the wave structures as compared with the N2+—Si system. However, continued sputtering with oxygen ions in the O2+—Si system, while increasing amplitude of the waves, results in a considerable deterioration of coherency and planarity of the structure. On the contrary, a wavelike pattern structure formed in N2+—Si is notable for a high degree of planarity extending to the sputtering depths equal to 3*DF.
A prior art system having a plasma electrode with a matrix of apertures for forming an ion beam matrix out of general plasma was described in a U.S. Pat. No. 6,486,480 and a paper (K. L. Scott, T.-J. King, M. A. Lieberman, K.-N. Leung “Pattern generators and microcolumns for ion lithography”—Journal of Vacuum Science and Technology B, v. 18 (6), 2000, pp. 3172-3176.) The system described in these references is not capable of producing the patterns with required minimum size.
Another prior art system for forming patterns on surfaces of wafers was disclosed in Russian Pat. No. RU 2,180,885. It has a block for forming a matrix of oblique linear ion beams implemented as a plasma electrode with the matrix of linear apertures positioned according to the required disposition of the arrays of nanolines on the silicon surface and a precision stage for transferring of a wafer across the sheet ion beams. However this device requires a complex system for controlling and focusing ion beams.
Therefore there remains a need for effective and relatively inexpensive techniques and devices for forming highly coherent wavelike nanostructures.